POS1324 THE IMPORTANCE OF MRI IMAGING FOR THE MANAGEMENT AND UNDERSTANDING OF THE DISEASE ORIGIN IN FIBRODYSPLASIA OSSIFICANS PROGRESSIVA
Authors: I. Nikishina, S. Arsenyeva, V. Matkava, M. Kaleda, T. Pachkoria, A. Arefieva
Journal: Annals of the Rheumatic Diseases (2022)

Background Fibrodysplasia ossificans progressive (FOP) is ultra-rare autosomal dominant inherited genetic disorder which is caused by mutation in ACVR1 gene and provokes severe heterotopic ossification (HO) as a «second skeleton disease». Our long-term experience of the largest group of FOP patients in single Russian center makes possible to interpretate clinical findings and imaging as the evidences that FOP may belong to special kind of axial spondyloarthritis. Because of new bones formation process X-Ray and CT scans recognize as the main imaging methods for the FOP. But MRI method may present important information for the understanding of the disease origin in FOP. Objectives To analyze the MRI findings in FOP patients in relation to clinical manifestations, and therapy options. Methods The study was based on retrospective and prospective observation and included 40 pts (21 males; 19 females). Diagnosis of FOP was established on typical clinical features and detecting mutation. X-ray, CT and MRI were performed in most patients excluding the severe disabled status of FOP. Some patients failed to perform MRI due to the presence of severe skeletal deformities or artificial metal constructions (because of previous orthopedic operations). Blood assessment has never shown specific elevated markers. Results Among of all 40 FOP patients MRI of sacroiliac joints was performed in 14 patients. Сhronic sacroiliitis was detected in 10/14 pts, including active sacroiliitis in STIR regimen in 6/14 pts by. Also 7/14 pts have MRI evidence of severe coxitis (see Figure 1). This imagines findings and other features of axial involvement (X ray imagines of ankylosis of the facet joints and vertebral bodies by the type of syndesmophytes) allowed us to establish alternative diagnosis of juvenile spondyloarthritis (JAS) in 7 pts and juvenile idiopathic arthritis (JIA) in 5 cases. It was needed for the legal possibility to administer tofacitinib (TOFA) in 12 pts (the youngest pt of 2 y.o, the oldest – 19 y.o) with strong uncontrolled progression of FOP. The dosage of TOFA was up to 5 mg twice a day. We noticed that all 12 pts have severe coxitis with synovia proliferation (with MRI and ultrasound evidence). Duration of TOFA therapy is from 2 to 25 months. Drug tolerance was good in all pts, no AE were registered. New nodes formation immediately stopped in most pts, significant improvement of motions was observed in 10 (83%) pts. Also, we noticed fast regression of sacroiliitis and coxitis activity by MRI in 5 (42%) pts under TOFA therapy. All other patients didn`t have repeated MRI examination yet. So MRI seems to be important method to confirm the anti-inflammatory effects for sacroiliitis and coxitis signs in patients with FOP. It seems to expect that inflammation control may prevent the sacroiliac and hip ankyloses. In spite of the absence of new HO in our 16 y.o. pt, we found continuous intraskeletal ossification between C3-C4, C5-C7 vertebral bodies, facet joints that leads to subtotal stenosis of spinal canal without any neurological symptoms. Because of «protection effect» of external heterotopic ossification severe neurological damage was not developed. Figure 1. Two different patients with severe FOP and similar evidences of sacroiliitis and bilateral hips synovitis by MRI Conclusion According to MRI findings, hip damage was characterized for all ages of FOP patients. Sacroiliitis we found mostly in patients older 10 y.o. Based on our experience of JAK-inhibitor therapy we can suggest about positive effect and advantages of TOFA over other therapy approaches. Dynamics of MRI imaging may be good option for the confirmation of therapeutic anti-inflammatory effects. Disclosure of Interests None declared